NIRAS has been providing expertise and advice to the offshore wind sector (OWS) for more than 30 years Offshore wind as a source of energy continues to improve on Cost of Energy (CoE)

There is a need within the OWS to understand the decommissioning of offshore wind farms (OWFs) to a greater extent. Planning for decommissioning holds unexplored possibilities for reducing the CoE if it is addressed as early as possible, even during the de-risking or design phase. Industries similar to the OWS have failed to seriously assess the actual cost of decommissioning in detail, prior to decommissioning, and have been surprised with the actual cost.

In 2014, NIRAS initiated the innovation project ODIN-WIND with the aim of developing an model and management tool for the full decommissioning process. The project also includes tools for estimating the remaining life of a OWF structure and a best practice guide for decommissioning OWFs. EUDP subordinating to the Danish Energy Agency, supports the project. Project partners are; Maersk Broaker, Vattenfall, DONG, DTU Energy and TWI. The project ends in mid-2017.

ODIN-WIND has made it possible for NIRAS to assist clients on offshore wind projects in regards to decommissioning. This on projects including initial feasibility, due-diligence evaluating existing parks and actual decommissioning plans for the final OWF phase.

This paper will present the result of the ODIN-WIND project and compare and elaborate on the knowledge gained through the work on actual projects, which has been used to update and calibrate the ODIN-WIND model.

Method

The ODIN-WIND tool assesses decommissioning through a detailed analysis of actual methods, logistics, environment, laws and legislation and weather-models. The cost estimate is made in CAPEX. This is in contrast to the more traditional viewpoint by simple reverse-engineering and assessment of cost as a multiple of the installation-cost.

The ODIN-WIND approach has been applied independently through the different phases that decommissioning can be addressed; feasibility, design phase, due- diligence and the actual decommissioning-plan. Relevant techniques and data have been collected from partners and experts. Methods, technology and data are all existing and field proven. This includes actual decommissioning-projects data.

The tool supports the development of a decommissioning-strategy, which is used for decommissioning-by-design (DbD) during the design-phase. The decommissioning-strategy is updated continuously thrugh the lifespan including commissioning and O&M.

Results

The ODIN-WIND approach has proven more accurate than traditional approaches to decommissioning in determining the actual cost of OWF decommissioning. The detailed and more accurate estimate that the ODIN-WIND tool provides are due to the fact that economic contingencies are replaced with actual costs as actual methods are used.

The approach provides a reduction of cost and thereby reduces the CoE, as the owner can allocate less funding for decommissioning. The improvement in CoE is also explained through the efficient interaction with the designers of the OWF structures and greater interaction and input with the operation and maintenance phase.

Conclusions

The ODIN-WIND approach to decommissioning improves the CoE of offshore wind. The benefit of addressing decommissioning early in the design phase is clear and is directly linked to reducing the cost of decommissioning. Furthermore the optimisation of decommissioning assists in reducing the environmental impact, reduces the use of resources and promotes circular economy.

Detailed decommissioning is especially beneficial for developing a useful decommissioning plan and guiding asset owners through the different phases. It also provides input to end of life (EoL) estimation, re-powering considerations, and the basis for an EIA.

The paper will clarify the importance of including decommissioning planning in good time for all phases of the OWF life cycle, as listed under Learning Objectives:

Objectives

The initial planning and feasibility-study and where a proper decommissioning-assessment will; give input to the selection of preferred design in regards to environment and cost, possible synergies with other trades and regional projects, secure recourses, prepare the supply-chain, give valuable input to the design and if conducted correctly providing valuable input to the O&M phase.

The due-diligence phase where an decommissioning-strategy can be compiled or an existing updated. It should assess or update methods, costs, legal matters, environment considerations and include potential synergies. This will support trade with OWF, estimates for required guaranties and mapping of the supply-chain.

The final stage of the windfarm where a final decommissioning-plan needs to be compiled. The earlier this is completed the more useful it is for the owner during final stage.